A Relationship Before Becoming A Real Item summary:

Shu is a high school student who lives with his baby brother, Yuto, and his dad. Trying hard to fill in for his mom after she died of an illness, Shu handles the cooking at home and takes care of Yuto. Shu secretly admires Kazuki, a kind, good-looking man and his first love who happens to be his brother's pre-kindergarten teacher. Shu's feelings for Kazuki are growing stronger by the day. They may not be one-sided in this sweet, tender love story about a high school boy with a pure heart who faces many challenges as he cherishes his love for his brother's teacher.